Submission #629117

#	Time	Username	Problem	Language	Result	Execution time	Memory
629117		Cyber_Wolf	Network (BOI15_net)	C++14	63 / 100	9 ms	13140 KiB

net

//Contest: BOI'15 Day 1 Problem 3
//Problem: Net
//Link: https://oj.uz/problem/view/BOI15_net

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("Ofast")

using namespace std;
using namespace __gnu_pbds;

#define lg long long
#define ordered_set	tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define error(args...) { string _s = #args; replace(_s.begin(), _s.end(), ',', ' '); stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args);
#define endl \n
#define lbound(x, y) lower_bound(x.begin(), x.end(), y) 
#define ubound(x, y) upper_bound(x.begin(), x.end(), y) 
#define sortasc(v) sort(v.begin(), v.end())	
#define sortdesc(v) sort(v.rbegin(), v.rend())	
#define custom_array(a,l, r) int _##a[r-l+1]; int*a=_##a-l;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const lg MOD = 1e9+7, N = 2e5+5, M = 1e7+1, SZ = 1e3+1;
/*
bitset<N> primes;
lg pwrs[N], inv[N];

lg fast_power(lg n, lg k)
{
	if(!k)	return 1;
	if(k&1)	return (fast_power(n, k-1)*n)%MOD;
	lg x = fast_power(n, k/2)%MOD;
	return (x*x)%MOD;
}

void sieve()
{
	primes.set();
	primes[0] = primes[1] = 0;
	for(lg i = 2; i < N; i++)
	{
		if(!primes[i])	continue;
		for(lg j = i*i; j < N; j += i)
		{
			primes[j] = 0;
		}
	}
	return;
}

struct matrix
{
	vector<vector<lg>> con = vector<vector<lg>> (SZ, vector<lg> (SZ));
	matrix operator *(const matrix& a)
	{
		matrix product;
		for(int i = 0; i < (lg)con.size(); i++)
		{
			for(int j = 0; j < (lg)a.con[0].size(); j++)
			{
				for(int k = 0; k < (lg)a.con.size(); k++)
				{
					product.con[i][j] = (product.con[i][j]+(con[i][k]*a.con[k][j])%MOD)%MOD; 
				}
			}
		}
		return product;
	}
};

void preprocess(lg x)
{
	inv[2e5] = fast_power(x, MOD-2);
	for(int i = 2e5-1; i > 1; i--)
	{
		inv[i] = (inv[i+1]*i)%MOD;
	}
	pwrs[0] = 1;
	for(int i = 1; i <= 2e5; i++)
	{
		pwrs[i] = (pwrs[i]*i)%MOD;
	}
	return;
}

*/
vector<lg> a, deg(N);
vector<lg> adj[N];

void dfs(lg src, lg par = -1)
{
	if(deg[src] == 1)	a.push_back(src);
	for(auto it : adj[src])
	{
		if(par == it)	continue;
		dfs(it, src);
	}
	return;
}

int main()
{
	fastio;
	lg n;
	cin >> n;
	for(int i = 0; i < n-1; i++)
	{
		lg u, v;
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
		deg[u]++;
		deg[v]++;
	}
	lg node, mxm_deg = -1;
	for(int i = 1; i <= n; i++)
	{
		if(deg[i] >= mxm_deg)
		{
			mxm_deg = deg[i];
			node = i;
		}
	}
	dfs(node);
	lg x = a.size();
	cout << (x+1)/2 << '\n';
	for(int i = 0; i < (x+1)/2; i++)
	{
		if(i+x/2 >= a.size())
		{
			cout << a[i] << ' ' << a.back() << '\n';
			break;
		}
		cout << a[i] << ' ' << a[i+x/2] << '\n';
	}

    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:131:12: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  131 |   if(i+x/2 >= a.size())
      |      ~~~~~~^~~~~~~~~~~
net.cpp:126:5: warning: 'node' may be used uninitialized in this function [-Wmaybe-uninitialized]
  126 |  dfs(node);
      |  ~~~^~~~~~

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 0 / 37